Thanks for your reply. What I am trying to determine is in the horizontal plane what is is the angle of view . I tought as the focal length gets longer the angle of field of view gets smaller, such as in a telephoto lens. I am working on a unique probelm where I have the aerial photos of a island and very recognizable features on the island and am trying to work back with the field of view angle how far away the plane was when it took the photo. Not sure this will work but I want to explore this idea.

Georges, I calculate that a 162 mm lens covers about 41 degrees on 120 mm. 120 mm is the length of a 4x5 film holder's long side, but since the K-20 used roll film its gate may be a little wider. If so, the horizontal angle is a little wider too.

Bruce, the War Department bought lenses, to specification, from a number of makers.

USAF continued the practice, with a twist. It sometimes bought lenses made to a design, e.g., Metrogons and 38/4.5 Biogons, from the low bidder, sometimes to a specification (focal length, maximum aperture, and coverage), e.g., three quite different lenses for the KA-16.